Fluorescence (stereo)microscopes that are equipped with high-output illumination devices which also emit in the ultraviolet spectral region are known. In addition to exclusively UV-protective filters in the observation beam path, further filter combinations are used as excitation filters in the illumination beam path in order to isolate the wavelength(s) necessary for the particular fluorochrome, and as barrier filters in the observation beam path in order to block that same excitation light. These matched filter combinations are preferably incorporated into changeable modules, so that a rapid changeover between different fluorescent excitation illuminations is possible.
An even faster changeover is made possible by the fact that filter inserts freely selectable by the user are introduced into a magazine switchable in manual or motorized fashion, or into a turret. Positions not loaded with filter combinations must be equipped by the user with so-called “dummies” that interrupt or attenuate the illuminating beam path, in order to prevent damage to the eyes or to an image recording device due to the unfiltered high light intensity.
Also belonging to the existing art is a mechanical device (blocking slider), described in EP-B1-1 010 030, for interrupting the illumination beam path during breaks in observation. This prevents bleaching of the observed specimens with no need to switch off the illumination device. A shutter, motion-coupled in accordance with EP-B1-1 010 030 to the changeable filter carrier, interrupts the beam path during the switchover, and clears it again in the individual working positions.
With the apparatuses described above, the microscope user is still not dependably protected from a situation in which a position of the changeable filter carrier not loaded with a filter insert is engaged, and a very high light intensity can travel onto the specimen and into the observer's eye and an image recording device.